There have been numerous attempts to develop a multi-ratio transmission capable of shifting under load over the past century. Potential applications for such a transmission system are numerous, including motor vehicles, human-powered vehicles, maritime craft, and even turbines for power generation.
U.S. Pat. No. 1,428,999 to Tygard discloses a transmission system with axially-engaging, concentric nestable rims for varying a drive pulley diameter. U.S. Pat. No. 2,827,795 to Caballeros discloses a similar design utilizing a conical-shaped array of pulley segments. U.S. Pat. Nos. 5,443,423 and 5,637,046, both to Ha, and U.S. Pat. No. 6,267,699 to Gruich disclose transmission mechanisms specifically designed for automotive and bicycle applications, respectively. Other technical approaches to the development of multi-ratio transmissions abound. The most common feature either two pulleys connected by an endless flexible member, with radially-moving members that vary the diameter of one or more pulleys; or pulleys comprised of opposing conical sheave halves between which the endless drive member is tensioned and compressed, to produce continuously variable ratio of power transmission by moving the opposing sheave halves axially in order to control the radius around which the endless drive member rides. Other manifestations utilize conical components with enhancements.
Certain mechanical problems persistently affect clutchless multi-ratio transmissions that limit their widespread utilization; specifically, the ability of such transmission systems to function at high speeds or under significant loads effectively and efficiently in practical applications. In addition, ratcheting, slippage, and tensioning problems can limit the commercial viability of such systems by decreasing their reliability, increasing wear, etc.
Accordingly, there is a need for a novel multi-ratio transmission.